Hi Frans
As usual, you haven't got a clue, and your arguments limp.
In your explanation you could do away with a lot of things around your
airplane, because if everyting goes well, you will not need them. Like
fuses, circuitbrakers, a second fuel pump, not needed in normal
circimstances. Maybe toys instead.
In very normal life the controller will run until the limit switches are
opened. Thats why they are there. If you don't understand that go and
ask somebody, i am tired of explaning basic stuff to somebody who is not
interested anyway.
The rest of your answer is total rubbish, can't even bother.
Is there somebody out there who can explain to this poor soul how it is
supposed to work?
Regards,
Jos
28.6.2011 0:39, Frans Veldman kirjoitti:
> --> Europa-List message posted by: Frans Veldman<frans@privatepilots.nl>
>
> On 06/27/2011 09:38 PM, Jos Okhuijsen wrote:
>> It's a pity Mark, that you have not checked the max DC specification of
>> those microswitches.
> The max DC specification of the switches is of little value. Max DC is
> mainly limited by the opening arc of the switches under load. In normal
> situations, the limit switches are never opened as the controller cuts
> the power long before the limit is reached. These switches are just
> sitting there all their life closed, waiting for a controller failure
> which is unlikely to happen anyway.
>
> In a previous statement you claimed that the run away was caused by
> failed micro switches. This is similar as claiming that you have had a
> trim servo run away because of a failing end stop in the trim servo.
> Such a claim would ignore the fact that the trim servo can only run
> away, with or without end stop, if something keeps feeding power to it
> after it reached the desired position. It would require a faulty cockpit
> switch or faulty pilot in addition. Similary: Your situation, even with
> shorted micro switches, could only occur if the controller or some other
> circuitry was failing at the same time: something was delivering power
> to the prop while it was already over the target RPM. Even then, this
> would never let the CB pop. There is only one controller and it can not
> give power to two opposite directions at the same time whatever failure
> mode you can devise.
>
> Someone asked whether you had modified the circuitry and you denied
> that. However in the archive (before the accident) I found a message
> where you wrote that you had the reverse circuitry modified to simplify
> the process of entering reverse (which is cumbersome in the original
> setup but maybe there was a reason for that), and if I recall it
> correctly a relay was used to switch the controller and feed power to
> the reverse ring of the prop at the same time.
>
> If this modified circuitry failed, it would explain fully what happened:
> While feeding unwanted power to the reverse ring of the prop the prop
> could reach 0 or negative angle because the reverse slip ring bypasses
> the limit switches (for logical reasons) AND the controller at the same
> time, and the CB would pop if the controller tried to reverse the engine
> polarity.
>
> The whole story of short circuited limit switches does not explain the
> problems in any way. I would be confident to operate the airplane with
> shorted limit switches AND shorted or busted diodes, as these items are
> never used while the controller is working properly.
>
> The function of the diodes is to allow the motor to run in the other
> direction once one of the limit switches opened (otherwise you could
> never recover from reaching the prop limit as the limit switch cuts ALL
> power to the prop). In normal operation the diodes are never used.
> Neither shorting them or opening them would affect the normal operation
> of the prop. Again, whether these diodes are fully up to specs wouldn't
> matter at all in normal situations as it is unlikely that any current
> will ever flow through them.
>
> Your situation further differs from standard configurations by using the
> scimitar blades, which are not pitch bias neutral under load but have
> strong aerodynamic resistance in one pitch direction. It could well be
> possible that changing the pitch in one way caused excessive current,
> while in the other direction the aerodynamic loads would try to changing
> the pitch even further, and maybe drive the blades over the limit
> causing the limit switches to open. And in such a situation it might be
> possible that the limit switches finally give up the ghost (but
> logically they would burn through and open up, making it impossible to
> change the pitch from there). Again, even in this scenario it would not
> lead to pitch run aways and popping CB's, but just to a prop which
> doesn't respond anymore to pitch change commands.
>
> Frans
>
>
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